Pollen from flowers and grasses often trigger seasonal allergy symptoms like sneezing and red, itchy eyes. When it comes to the cannabis plant, there is plenty of research indicating how marijuana can combat allergies as an anti-inflammatory both topically and for respiratory issues. But there is much less information as to how and why marijuana can cause allergies.
People in high exposure environments, like trimmers, often report things like itchy eyes and runny noses when dealing directly with the fresh plant material. These symptoms mimic allergic reactions, but there isn’t a clear answer when it comes to the exact compounds in cannabis that might be the cause.
“I can’t say I’ve ever had a strain that made me sneeze although sticking my face in a big bag of Diesel definitely gives my nose a tickle,” says cannabis expert and comedian Ngaio Bealum, from Netflix’s Cooking on High.
The question is as complex as the cannabis plant itself. There are thousands of specific cultivars and dozens of strain families. In each bud, there are dozens of aroma molecules called terpenes, plus the cannabinoids—the THC, CBD, and other molecules that also shape the effect. Each strain offers a unique chemical fingerprint of compounds that each person’s uniquely tuned immune system reacts to.
Potential allergens: cannabis pollen, terpenes
Cannabis is a dioecious plant, meaning it appears in both male and female forms. Male cannabis plants produce pollen, a common cause of seasonal allergies, so it makes sense that cannabis pollen could cause allergic reactions for some people. But unless you’re a breeder, you are unlikely to come into contact with much cannabis pollen in the natural world.
When it comes to what might be causing allergies through breathing, inhaling, ingesting or touching female marijuana plants and flowers, the conversation gets much more complicated.
“Like any natural substance, cannabis or cannabis constituents in some sensitive people can certainly produce allergic symptoms ranging from very mild, like a sneeze, to more severe skin reactions or even respiratory reactions,” says Uwe Blesching, co-founder and Chief Science Officer of Cannakeys, and author of Your Cannabis CBD: THC Ratio.
“Yes, of course, people can be allergic to cannabis, but the challenge you have is to determine if it’s a true allergic reaction to cannabis, or is it a reaction that mimics allergic-like symptoms, or is it an allergic reaction to potential contaminants that made it into the plant?”
Personal chemistry vs. pesticides, fertilizers, mold?
Blesching explains further that allergens associated with cannabis exposure, like a skin rash, could be caused by other underlying causes such as something a person ate.
Or, they could be caused by a pesticide, synthetic fertilizer or a number of different materials that the plant has either been covered in or absorbed.
“… every time I touched Dutch Treat my arms would welt up.”
Sara Payan, Public Education Officer, The Apothecarium
If it were possible to narrow down the cause of allergies associated with cannabis to the plant itself, the next step would be to hone in on which element or elements of the plant’s more than 800 natural components could cause the irritation.
“It ultimately comes down to the individual’s vulnerability to whatever one, or combination of compounds they’ve been exposed to that’s causing the trigger,” Blesching says. “I don’t think anyone can tell at this point which components are most likely to be the culprits. Terpenes are certainly a top contender, but so could be the rhizomes and cannabinoids.”
- When it comes to terpenes, linalool appears to be the most studied in its potential to be a common contact allergen.
- When it comes to potential pesticides being the culprit, neem oil used on cannabis to prevent pests could also be a trigger.
- Studies show an allergic reaction to cannabis may also be involved with lipid transfer proteins found in cannabis as well as fruits, vegetables, nuts, pollen, and latex.
- And, of course, smoke in general, or moldy cannabis can also cause adverse allergic reactions.
A closer look at terpenes
I grew cannabis for the first time in the great lull that was 2020 and found that—like the fragrant heirloom tomatoes I was also growing in my backyard garden—when my arms brushed up against my weed plants, I got a mild skin rash. Many people who work in the cannabis industry have similar stories and current studies that examine cannabis allergies primarily focus on those within the industry that have a high exposure to plant material for an extended time, such as trimmers.
“In my experience [an allergic reaction to cannabis] depends on your personal makeup rather than individual cultivars,” says Sara Payan, public education officer at the Apothecarium. “For example, before pre-packaged cannabis, we would fill the jars from our bulk stock and every time I touched Dutch Treat my arms would welt up.”
One Leafly editor got the sneezes every time he trimmed his super-fragrant Squirt strain after the 2020 harvest.
Dr. Laurie Vollen of Naturally Healing MD says that she knows cannabis allergies have been reported in scientific literature but has not seen it with the patients she has treated, which is upwards of 13,000 people.
Terpene allergy tests lacking
Allergies to cannabis, she says, are also challenging to determine via the traditional skin prick tests because the tests must be conducted using raw material. Cannabis terpenes—especially the unique and delicate monoterpenes—are at their most prominent in fresh plants, but studies show, “this approach is virtually impossible to standardize, mainly because of unpredictable variations in composition and potential contaminations with other allergens of the raw material.”
For example, monoterpenes boil off at room temperature—that’s the bright, sharp fragrance you smell on a pot farm.
“The terpenes are the most volatile part of the plant, so if you administer a test you have to go to great lengths to make sure the terpenes are present and that’s not what they are trying to do,” she says. “They are trying to link [cannabis allergies] to the THC and the CBD.”
Other plant allergies causing cross-reactivity
Although the use of cannabis dates back to ancient times, the first description of a cannabis allergy did not appear until 1971. It involved a 29-year-old housewife who suffered from an allergic reaction after smoking a “marihuana cigarette.” Back then, the potential culprit being considered was THC, but today studies suggest a link to cross-reactions with other things that cause allergies.
“If you have an allergy to cannabis you might have a cross allergy to another plant and that suggests to me that it’s not the phytocannabinoids because you don’t see those in other plants, but it’s the terpenes,” Vollen says.
Blesching speculates that the key to cannabis causing allergies is likely more associated with an individual’s sensitivities rather than a link to specific cultivars or strain families. Typically, he says, the people who already have adverse reactions to other types of plants will be the ones most likely affected by cannabis allergens.
“People whose noses are at war with plants, they are the ones, ‘Oh yeah, I sneeze when I’m around it,’” he says. “I think there’s something wrong with people’s sensitivity scale… some people’s immune system is so overactive that they react to nature, so I think the pathology lies with the patient, rather than the culprit being a piece of nature.”